Data communication networks are being developed which enable the flow of information to ever greater numbers of users at ever higher transmission rates. However, data transmitted at high rates in multi-pair data communication cables has an increased susceptibility to crosstalk, which often adversely affects the processing and integrity of the transmitted data. The problem of crosstalk in information networks increases as the frequency of the transmitted signals increases.
In the case of local area network (LAN) systems employing electrically distinct twisted wire pairs, crosstalk occurs when signal energy inadvertently "crosses" from one signal pair to another. The point at which the signal crosses or couples from one set of wires to another may be 1) within the connector or internal circuitry of the transmitting station, referred to as "near-end" crosstalk, 2) within the connector or internal circuitry of the receiving station, referred to as "far-end crosstalk", or 3) within the interconnecting cable.
Near-end crosstalk ("NEXT") is especially troublesome in the case of telecommunication connectors of the type specified in sub-part F of FCC part 68.500, commonly referred to as modular connectors. Such modular connectors include modular plugs and modular jacks. The EIA/TIA of ANSI has promulgated electrical specifications for near-end crosstalk isolation in network connectors to ensure that the connectors themselves do not compromise the overall performance of the unshielded twisted pair interconnect hardware typically used in LAN systems. The EIA/TIA Category 5 electrical specifications specify the minimum near-end crosstalk isolation for connectors used in 100 ohm unshielded twisted pair Ethernet type interconnects at speeds of up to 100 MHz.
High speed data transmission cable typically comprise four circuits defined by eight wires arranged in four twisted pairs. The cable is typically terminated by modular plugs having eight contacts, and specified ones of the four pairs of the plug contacts are assigned to terminate respective specified ones of the four cable wire pairs according to ANSI/EIA/TIA standard 568B. The four pairs of plug contacts in turn engage four corresponding pairs of jack contacts. In particular, the standard 568B contact assignment for the wire pair designated "1" is the pair of plug and jack contacts located at the 4-5 contact positions. The cable wires of the pair designated "3" are, according to standard 568, terminated by the plug and jack contacts located at the 3-6 positions which straddle the "4-5" plug and jack contacts that terminate wire pair "1". Near-end crosstalk between wire pairs "1" and "3" during high speed data transmission has been found to be particularly troublesome in connectors that terminate cable according to standard 568.
While it is desirable to use modular connectors for data transmission for reasons of economy, convenience and standardization, such connectors generally comprise a plurality of identically configured electrical contact/terminal members that extend parallel and closely spaced to each other thereby creating the possibility of excessive near-end crosstalk at high frequencies. Specifically, modular jacks generally include a plurality of unitary contact/terminal members made of conductive material and formed to provide a corresponding plurality of closely spaced, substantially parallel contact portions which are adapted to be engaged by blade-like contacts of the modular plugs. Each contact/terminal member is formed to further provide a pin-like terminal portion and an intermediate portion interconnecting the contact and terminal portions. The terminal portion can be connected to the circuit of a printed circuit board. When a modular plug is inserted into the receptacle of a modular jack, the contact blades of the plug engage respective contact portions of the contact/terminal members of the jack. The signals flowing through the contact/terminal members of each transmission circuit create electromagnetic and inductive fields which undesirably couple to other circuits resulting in near-end crosstalk.
Since it has been appreciated that the identical configuration of the contact/terminal members causes crosstalk, several fundamentally different techniques have been developed to vary the shape of the contact/terminal members and thereby reduce crosstalk. A first technique, exemplified by U.S. Pat. Nos. 5,639,266 and 5,791,942 (Patel), incorporated by reference herein, is to form the contact/terminal members so that selective contact portions are forward facing while others are rearward facing while maintaining the contact/terminal members substantially parallel to one another. More particularly, the connector described in the '266 patent includes a contact/terminal member having a contact portion having a free end situated near and facing toward a front of the receptacle ("a forward facing contact portion"), and a contact/terminal member having a contact portion having a free end situated near and facing toward the closed end of the receptacle ("a rearward facing contact portion") whereby the contact/terminal member with the forward facing contact portion inherently has a different shape than the contact/terminal member with the rearward facing contact portion. Crosstalk is reduced by virtue of the different geometry of the contact/terminal members.
A second technique is to construct the contact/terminal members to physically cross-over one another and is exemplified by U.S. Pat. No. 5,362,257 (Neal et al.). In the '257 patent, each contact/terminal member is arranged to cross-over an adjacent contact/terminal member at least once to thereby reduce near-end crosstalk.
Furthermore, as the size of electronic components has become reduced with advances in semiconductor technology, it has become increasingly necessary to increase the number of modular connector ports which can be mounted within a given area.